Use reasoning_content instead of reasoning

Author: aldehir

codex-rs/core/src/chat_completions.rs

@@ -208,7 +208,7 @@ pub(crate) async fn stream_chat_completions(
                     && let Some(reasoning) = reasoning_by_anchor_index.get(&idx)
                     && let Some(obj) = msg.as_object_mut()
                 {
-                    obj.insert("reasoning".to_string(), json!(reasoning));
+                    obj.insert("reasoning_content".to_string(), json!(reasoning));
                 }
                 messages.push(msg);
             }
@@ -233,7 +233,7 @@ pub(crate) async fn stream_chat_completions(
                 if let Some(reasoning) = reasoning_by_anchor_index.get(&idx)
                     && let Some(obj) = msg.as_object_mut()
                 {
-                    obj.insert("reasoning".to_string(), json!(reasoning));
+                    obj.insert("reasoning_content".to_string(), json!(reasoning));
                 }
                 messages.push(msg);
             }
@@ -257,7 +257,7 @@ pub(crate) async fn stream_chat_completions(
                 if let Some(reasoning) = reasoning_by_anchor_index.get(&idx)
                     && let Some(obj) = msg.as_object_mut()
                 {
-                    obj.insert("reasoning".to_string(), json!(reasoning));
+                    obj.insert("reasoning_content".to_string(), json!(reasoning));
                 }
                 messages.push(msg);
             }
@@ -593,7 +593,7 @@ async fn process_chat_sse<S>(
             // Forward any reasoning/thinking deltas if present.
             // Some providers stream `reasoning` as a plain string while others
             // nest the text under an object (e.g. `{ "reasoning": { "text": "…" } }`).
-            if let Some(reasoning_val) = choice.get("delta").and_then(|d| d.get("reasoning")) {
+            if let Some(reasoning_val) = choice.get("delta").and_then(|d| d.get("reasoning_content")) {
                 let mut maybe_text = reasoning_val
                     .as_str()
                     .map(str::to_string)
@@ -622,7 +622,7 @@ async fn process_chat_sse<S>(
             }
 
             // Some providers only include reasoning on the final message object.
-            if let Some(message_reasoning) = choice.get("message").and_then(|m| m.get("reasoning"))
+            if let Some(message_reasoning) = choice.get("message").and_then(|m| m.get("reasoning_content"))
             {
                 // Accept either a plain string or an object with { text | content }
                 if let Some(s) = message_reasoning.as_str() {